Reciprocating tools that are motor driven, such as saber saws, larger reciprocating saws and the like are usually driven by electric motors that have a rotating output shaft. The rotating motion is translated into reciprocating motion for moving a saw blade or the like in a reciprocating manner. Various approaches have been developed which translate the rotation motion into reciprocating motion. A common approach is the incorporation of a wobble plate drive.
A “wobble plate” assembly is a configuration wherein a shaft has an angled portion on which an arm is mounted through a ball bearing assembly. The arm is slidingly positioned within a portion of a plunger assembly. As the angled portion of the shaft rotates, the arm translates the rotation of the shaft into a reciprocating movement of the plunger assembly. One example of a reciprocating tool which incorporates a wobble plate drive is U.S. Pat. No. 7,707,729, which issued on May 4, 2010, the entire contents of which are herein incorporated by reference.
In addition to a reciprocating movement, some reciprocating tools include an orbital movement. This is accomplished by allowing the plunger of the tool to be pivoted, and driving a pivoting movement of the plunger with the motor of the tool. Such orbital movement increases the sawing efficiency of the tool.
In some reciprocating systems, however, the mechanism which is used to effect orbital movement does not force orbital movement throughout a complete reciprocation of the tool. Such partial orbital movement reduces the potential efficiency of the tool. The partial orbital movement in some instances is caused by a phenomenon known as “cam floating”.
In systems exhibiting cam float, a cam is used to pivot the plunger. In order to transfer force from the cam to the plunger, a spring is used to bias a cam follower against the cam. At high speeds, however, internal oscillations can be developed within the spring which reduces the effective force applied by the spring. The reduced effectiveness of the spring results in a loss of contact between the cam and the cam follower which can be referred to as “cam floating”. To overcome can floating, a spring with a higher spring constant can be incorporated into the device. The increased frictional forces between the cam and the cam follower which are generated by a spring with a higher spring constant increase the wear of the system. Additionally, more power is required to overcome the increased friction. In systems incorporating a battery, the need for increased power significantly reduces the power available for cutting operations as well as the useful charge.
A need exists for a reciprocating tool which provides orbital movement throughout an entire reciprocating cycle of the tool. A further need exists for a reciprocating tool which provides orbital movement without unduly increasing the power required to operate the tool.